1. Field of the Invention
This invention relates to a method for machining metal work, and more particularly to an improvement in a method for machining metal work which have thereon an image marked off by a photographic process.
2. Description of the Prior Art
A photographic marking-off process usng a diazo photosensitive layer has been in use for a considerable period of time in the aircraft manufacturing industry. Furthermore, with the advancement of electrophotographic technology, the application of electrophotography to a marking-off process has become widespread in the shipbuilding industry in the last ten years.
When fine and highly precise marking lines are required, it becomes necessary to form a photosensitive layer on the surface of the work to be marked off. Suitable materials for the layer include a diazo photosensitive layer, photosensitive resin layers and electrophotographic sensitive layers. Moreover, it has become possible for the photosensitive material to be left only at the marked portion and to be removed at the non-image portion by effectively utilizing recently developed processes such as particle migration recording methods (as disclosed, for example, in U.S. Pat. No. 3,520,681, Japanese Patent Publication Nos. 10796/1968 and 13513/1968, and British Pat. No. 1,152,365), photoelectrophoretic recording methods (as disclosed, for instance, in U.S. Pat. No. 3,384,565, Japanese Patent Publication No. 21781/1968 and British Pat. No. 1,124,625) and manifold recording methods (as disclosed, for instance, in U.S. Pat. No. 3,512,968), thus increasing the desirability from the standpoint of subsequent fabrication. Also, when high precision is not of primary importance, a method according to Japanese Patent Publication No. 122195/1972 can be suitably utilized.
Conventionally, a layout requiring high precision has been scribed using a marking-off pin.
The advantages of mechanically marked-off images include resistance against erasure during the subsequent machining operation and the ease in applying punches at crucial points of the grooves which form the images, the advantages usually outweighing the disadvantage that the images are sometimes difficult to view due to reflection.
In contrast, photographically marked-off images are generally formed by addition of a certain material, resulting in image-bearing surfaces which either protrude or are substantially flat. While good visibility to the naked eye is obtained, photographically produced images can easily be removed from the image-bearing members or from the photosensitive layers thereof, or may in other instances simply disintegrate during the subsequent fabrication. The images may also deteriorate due to the high temperature produced during the machining of hard image-bearing members or under the influence of solvents such as kerosene used for oil-immersion electrospark machining, making it necessary to specifically protect the images in these cases.
A bath for electrospark machining usually contains minute metal powder particles and other floating dust which are electrostatically charged and tend to contaminate the background of the recording layer.
A possible method to protect a recorded image is to provide a protective layer coating which does not hinder seeing the image. Conventionally used protective layers, however, either tend to soften upon heating or have highly insulating properties, which mean dust particles in the electrospark bath are electrostatically attracted to the layer.